The broad goal of this research is to better understand the functioning of the human auditory system, both in its normal state and in the temporarily abnormal state induced by exposure to intense sound. Among the various questions to be addressed by individual experiments are: (1) the relative susceptibilities of low- and high-frequency regions to temporary threshold shift (TTS) and temporary loudness shift (TLS), (2) the way contralateral stimulation of varying frequency and intensity affects ipsilateral TTS, (3) the way loudness functions are altered at frequencies remote from the exposure frequency, (4) the various ways temporal processing is upset following exposure to intense sound or ingestion of aspirin, and (5) the ways oto-acoustic emissions respond to "exposures" of various frequencies and intensities. Knowledge about these issues will not only contribute to a fuller understanding of the auditory system, but it may also prove relevant to the establishment of guidelines or standards for exposure to intense sounds in occupational and recreational settings. The research is also relevant to investigators interested in model conditions for sensorineural hearing loss. Various psychophysical methods will be used in the different experiments. Loudness is measured using variants of the alternate binaural loudness balance (ABLB) procedure. Sensitivity in the quiet is measured using a form of the classical method of adjustment or using adaptive two-interval forced-choice. The standard procedure is to measure hearing sensitivity and whatever other psychophysical ability is of interest prior to any exposures to intense sound, deliver an intense sound that is calibrated to produce a known amount of TTS, and then measure both the recovery from TTS and the other psychophysical ability of interest. Our exposure intensities and durations are calibrated for each subject individually to produce 12-14 dB of TTS, and no exposure exceeding 110 dB for 15 mins is ever given. In some experiments we plan to use a technique of successive, short exposures rather than one longer one; the goal is to hold the level of auditory "fatigue" at a known, fixed value in order to study it better. The informed consent procedure includes an educational program of required lectures, films, and readings.